Tunable and switchable erbium-doped fiber laser based on parallel dual Lyot filters cascaded with a Sagnac loop

In this paper, a tunable and switchable erbium-doped fiber laser (EDFL) based on parallel dual Lyot filters cascaded with a Sagnac loop is proposed. The filter can be regarded as a composite filter, whose structure is composed of cascaded different filters to ensure the presented tuning range and flexibility of parameter configuration. The wavelength resolution and polarization stability of the filter are enhanced by the synergistic effect of the multistage polarization-maintaining fibers (PMFs) and polarization controllers (PCs). The experimental results show that when the pump power is 250 mW and the lengths of the PMFs used are 4 m, 4 m, and 8 m respectively, the wavelength spacing can be adjusted by tuning the three PCs in the filter, allowing the laser to be reconfigured to alter the polarization state, thereby achieving continuous excitation of 1 to 7 wavelengths in the range from 1530.52 nm to 1568.04 nm. In addition, the output wavelength is adjustable over a range of ∼37.52 nm. The side-mode suppression ratios for the output wavelengths of this laser all exceed ∼41.60 dB. The proposed EDFL has good tunability, switchability, and stability.